Electrodeposition of nickel and nickel alloys



United States PatentO "ice ELECTRODEPOSITION F NICKEL AND NICKEL ALLOYS Walter Cowle, Crayford, Donald Eugene Mansfield and Peter Spiro, London, and George Charles .Wood, Ashtead, England, assignors to S. A. Vickers Limited, London, England, a British company No Drawing. Application December 7, 1954, Serial No. 473,724

Claims priority, application Great Britain December 10, 1953 8 Claims. (Cl. 204-43) The present invention refers to electrodepositing nickel or nickel alloys on conductors or non-conductors to any required thickness.

Among the objects of the present invention is the deposition of metal with a thickness as even as possible however intricate the cathode is in shape. Other objects are that the deposited metal should have low stress and should be hard.

According to the invention, an electrolytic bath is employed which includes a nickel salt and sodium or potassium chloride and in which the amount of sodium or potassium chloride is several times greater by weight than the amount of nickel present in the nickel salt. Previously, it has been usual to employ a small amount of sodium chloride of the order of 2-4 ozs. per Imperial gallon as an ingredient in nickel plating solutions to act as a conducting salt and to increase the corrosion of the anodes. Such small quantities of sodium chloride in the presence of a large amount of nickel act as powerful stress raisers and, as the smallest increment still further raises the stress, care has usually been taken to keep the amount of sodium chloride small compared with the weight of nickel.

An arbitrary test of throwing power is to compare the weight of deposit on an angular test piece per unit area at the centre and at the extreme edges and using such a test to compare the throwing power of various electrolytic baths. It was found that using a bath in accordance with the invention, including a nickel salt and sodium or potassium chloride several times greater than the amount by weight of nickel, a throwing power is obtained which is several times greater than the throwing power of high nickel, low chloride baths, containing a fluoride, which in turn have a higher throwing power than that obtained with all other well known baths and than could be obtained by following known expedients for increasing throwing power, such as adding sodium or manganese sulphate or sodium citrate to the bath, or just reducing the nickel content.

It has now been ascertained that the combination in an electrolytic bath of a low weight of nickel and a comparatively much larger weight of sodium chloride in accordance with our invention causes a superior throwing power as described above, reasonably low stress in the deposit, good physical properties of the deposit, apart from other advantages, the main point however being the degree of evenness to an extent previously unknown, as far as nickel deposits were concerned in the thickness of not only thin but also substantial deposits, where the cumulative effects of limited throwing power are reduced.

The ratio of weight of sodium chloride to weight of nickel contemplated is of the order of 8:1, the nickel of course being added in the form of a nickel salt.

In our preferred way of operating the invention, 3 to 4 ozs. of nickel added as nickel sulphate or sulphamate together with 30-35 ozs. of sodium chloride and up to 5 Patented Aug. 13, 1957- 2 ozs. of boric acid are made up to one gallon of solution with water. 4 ozs. of nickel would mean approximately 16 /2 ozs. of nickel sulphate or 19 ozs., depending on whether the grade with 4 or with 7 molecules of water crystallisation per molecule of nickel is used. In addition, a known wetting agent is employed.

It should be noted that the concentrations specified in this specification and in the appended claims refer to the British or Imperial gallon, which is approximately equal to 1.2 U. S. gallons.

Where in this specification reference is made to sodium salts, potassium salts can be used.

The preferred temperature of operation is 40 C. in the plating solution.

The preferred current density is 15 amps. per sq. ft., though the bath operates satisfactorily between 10 and 20 amps. per sq. ft. or higher with agitation. This is another advantage of the invention. All nickel plating solutions investigated reach their optimum throwing power at a comparatively low current density, usually below 10 amps. per sq. ft., though for commercial reasons plating solutions are often operated at higher current densities, thus sacrificing throwing power, which on some plating work is not so essential. Beyond the current density at which optimum throwing power is reached, the latter declines very steeply with every increase in current density. However, the solution employed in the present invention, when operated at the preferred conditions described above, reaches its optimum throwing power following the test described above at 15 amps. per sq. ft. The curve of throwing power against current density is nearly flat, though rising slightly, between 10 and 15 amps. per sq. ft., and even between 15 and 20 amps. per sq. ft. the decline is very limited, the throwing power still being of a high order at 20 amps. per sq. ft.

The relation between throwing power, hardness and pH value is somewhat intricate, and for optimum results we prefer a pH value of 2-5.

Another advantage of the solution according to the present invention is its relative transparency due to its low metal content, which greatly facilitates the inspection of objects being plated without lifting them out of the solution.

As in other plating solutions, the stress in the deposit produced when using the solution forming the subject of the present invention can be reduced to zero by means known in the art, such as organic stress reducers, such as saccharin, or superimposed alternating current. In this connection, a further helpful characteristic of the solution is that the stress in the deposit decreases with increasing cathode current density, whereas in all other plating solutions the opposite is the case. This has several operating advantages and reduces the danger of cracking or peeling deposits on projecting points where the current density is above the nominal average.

The hardness of the nickel produced, under conditions so far described, varies between 350 vickers at points where projections on the cathode caused the current density to be above the average and 440 vickers at the recessed points where deposition consequently took place at a current density below average.

A more even distribution of hardness at a figure ranging from 440 to 470 vickers is achieved by the addition of cobalt to the electrolyte in the form of a cobalt salt giving a cobalt content of between 5-15 grammes per gallon.

We claim:

1. An electrolytic bath for use in the electrodeposition of a metal selected from the group consisting of nickel and nickel-base alloys which comprises an aqueous solution of a nickel salt selected from the group consisting of nickel sulphate and nickel sulphamate and an inorganic chloride selected from the group consisting of sodium chloride and potassium chloride, in which the amount of nickel salt is equivalent to a nickel concentration of at least 3.0 ozs. per gallon and the amount of inorganic chloride is approximately eight times greater by weight than the amount of nickel present in the nickel salt.

2. An electrolytic bath for use in the electrodeposition of a metal selected from the group consisting of nickel and nickel-base alloys which comprises an aqueous solution of a nickel salt selected from the group consisting of nickel sulphate and nickel sulphamate and an inorganic chloride selected from the group consisting of sodium chloride and potassium chloride, in which the amount of nickel salt is equivalent to a nickel concentration of at least 3.0 ozs. per gallon and the amount of inorganic chloride in the bath is at least eight times greater by weight than the amount of nickel present in the nickel salt and in which the bath has a pH of from 2 to about 5.

3. An electrolytic bath for use in the electrodeposition of a metal selected from the group consisting of nickel and nickel-base alloys which comprises an aqueous solution of 34 ozs. per gallon of nickel present in the form of a nickel salt selected from the group consisting of nickel sulphate and nickel sulphamate, 30-35 ozs. per gallon of sodium chloride and up to 5 ozs. per gallon of boric acid.

4. An electrolytic bath for use in the electrodeposition of a nickel-cobalt alloy, which comprises an aqueous solution of a nickel salt selected from the group consisting of nickel sulphate and nickel sulphamate in a concentration equivalent to 34 ozs. per gallon of nickel, an inorganic chloride selected from the group consisting of sodium chloride and potassium chloride in a concentration of 30-35 ozs. per gallon, up to 5 ozs. per gallon of boric acid and a cobalt salt in a concentration equivalent to 5-15 grammes per gallon of cobalt, the electrolytic bath having a pH in the range of 2 to 5.

5. A method of electrodeposition of a metal selected from the group consisting of nickel and nickel-base alloys, which comprises applying direct current to an electrolytic bath which includes a nickel salt selected from the group consisting of nickel sulphate and nickel sulphamate and an inorganic chloride selected from the group consisting of sodium chloride and potassium chloride, the nickel salt being present in an amount equivalent to a nickel concentration of at least 3.0 ozs. per gallon and the inorganic chloride being present in an amount approximately eight times greater by weight than the amount of nickel in the nickel salt, and saccharin as an inorganic stress reducer.

6. A method of electrodeposition of a metal selected from the group consisting of nickel and nickel-base alloys, which comprises applying direct current at an average current density exceeding 10 amps. per square foot to an electrolytic bath which includes a nickel salt selected from the group consisting of nickel ulphate and nickel sulphamate and provided in an amount equivalent to a nickel concentration of at least 3.0 ozs. per gallon and an inorganic chloride selected from the group consisting of sodium chloride and potassium chloride and provided in an amount approximately eight times greater by weight than the amount of nickel present in the nickel salt and superimposing stress-reducing alternating current upon the direct current.

7. A method of electrodeposition of a metal selected from the group consisting of nickel and nickel-base alloys which comprises applying direct current at an average current density of 15 amps. per square foot to an electrolytic bath comprising an aqueous solution at pH 2 to 5 of nickel sulphate in a concentration equivalent to 3-4 ozs. per gallon of nickel, sodium chloride in a concentration of 30-35 ozs. per gallon and boric acid in a concentration of 5 ozs. per gallon.

8. A method of electrodeposition of a metal selected from the group consisting of nickel and nickel-base alloys which comprises applying direct current at an average currentdensity exceeding 20 amps. per square foot to an electrolytic bath comprising an aqueous solution at pH 2 to 5 of nickel sulphate in a concentration equivalent to 3-4 ozs. per gallon of nickel, sodium chloride in a concentration of .3 0-35 ozs. per gallon and boric acid in a con centration of 5 ozs. per gallon and agitating the electrolytic bath during electrodeposition therefrom.

Wesley et al.: Transactions Electrochemical Society, vol. (1939), pp. 233-4. 

1.AN ELECTROLYTIC BATH FOR USE IN THE ELECTRODEPOSITION OF A METAL SELELCTED FROM THE GROUP CONSISTING OF NICKEL AND NICKEL-BASE ALLOYS WHICH COMPRISES AN AQUEOUS SOLUTION OF A NICKEL SALT SELECTED FROM THE GROUP CONSISTING OF NICKEL SULPHATE AND NICKEL SULLPHAMATE AND AN INORGANIC CHLORIDE SELECTED FROM THE GROUP CONSISTING OF SODIUM CHLORIDE AND POTASSIUM CHLORIDE, IN WHICH THA AMOUNT OF NICKEL SALT IS EQUIVALENT TO A NICKEL CONCENTRATION OF AT LEAST 3.0 OZS. PER GALLON AND THE AMOUNT OF INORGANIC CHLORIDE IS APPROXIMATELY EIGHT TIMES GREATER BY WEIGHT THAN THE AMOUNT OF NICKEL PRESENT IN THE NICKEL SALLT. 